Polymeric flocculant and method of sludge dehydration

ABSTRACT

The invention provides a flocculant which in sludge dewatering gives flocs having an excellent balance among flocculating strength, filtration rate and moisture content, and a method of sludge dewatering with the flocculant.  
     Namely, the flocculant is a polymeric flocculent which contains a copolymer having alkoxyalkyl units or a poly(alkylene oxide) unit and further having water-soluble monomer units; and the method of sludge dewatering includes adding the polymeric flocculant to a sludge after or without adding an inorganic flocculent or an organic cationic compound thereto and then dewatering the sludge.

TECHNICAL FIELD

[0001] The present invention relates to a polymeric flocculant which isfor use in flocculation in sludges resulting from municipal sewage,industrial wastewaters, and the like and attains a high dewateringefficiency, and to a method of sludge dewatering with the flocculent.The invention falls under techniques for producing chemical products andtechniques for wastewater/sludge treatment.

BACKGROUND OF THE INVENTION

[0002] Various flocculants have hitherto been widely used for theflocculation/dewatering of sludges resulting from municipal sewage,industrial wastewaters, and the like.

[0003] For example, a method which comprises using poly(iron sulfate) asan inorganic flocculant, adding a nonionic, anionic, or cationicpolymeric flocculent alone thereto to form flocs, and dehydrating theflocs (Japanese Patent Laid-Open No. 51998/1983) and a method of sludgedewatering which comprises using an inorganic flocculant and anamphoteric polymeric flocculant having a cationic nature and an anionicnature (Japanese Patent Laid-Open No. 16599/1984) have been proposed.Other techniques include a method comprising adding an inorganicflocculent, subsequently adjusting the pH to 5 to 8, and adding anamphoteric polymeric flocculant thereto (Japanese Patent Laid-Open No.158200/1988).

[0004] Furthermore, known from long ago are a flocculent characterizedby comprising a polymer salt consisting of a poly(carboxylic acid) whichis partly or wholly in the form of a salt with a cationic surfactanthaving 6 or more carbon atoms (Japanese Patent Publication No.1729/1967) and a flocculant comprising an anionic copolymer comprisingas essential components acrylic acid and an alkyl acrylate, e.g., methylacrylate (Japanese Patent Laid-Open No. 41281/1974). Moreover, a sludgedehydrant comprising an amphoteric copolymer comprising a cationicmonomer, an anionic monomer, a water-soluble nonionic monomer, and ahydrophobic acrylic acid derivative having a solubility in water of 1 gor less, e.g., a (meth)acrylic acid alkyl ester having 8 or more carbonatoms, as essential components (Japanese Patent Laid-Open No.156400/1999) and the like have recently been proposed.

[0005] However, there have been cases where even with such variousflocculants and dewatering methods, a sufficient effect cannot beobtained depending on the kind of the sludge to be treated.

[0006] The techniques for flocculation/dewatering according to thevarious proposals described above have merits in their own ways and areused. However, with recent changes in the living environment and withthe resultant increase in the amount of sludges from municipal sewageand industrial wastewaters, the amount of the flocculants and dehydrantsto be used is increasing and this poses a problem. There is hence astrong desire for a flocculant or sludge dehydrant which, when used in asmaller amount, enables efficient flocculation/dewatering, i.e., whichhas better performance.

[0007] The present inventors made investigations in order to provide aflocculant and a method of sludge dewatering which, in sludgedewatering, give flocs having an excellent balance among flocculatingstrength, filtration rate, and moisture content and which can meet thedesire.

DISCLOSURE OF THE INVENTION

[0008] As a result of intensive investigations made by the presentinventors in order to eliminate the problem described above, it has beenfound that when a copolymer having alkoxyalkyl units or a poly(alkyleneoxide) unit and further having water-soluble-monomer units is used inthe dewatering of a sludge, flocs excellent in flocculating strength,moisture content, and filtration rate can be obtained. The inventorshave made it possible to provide an excellent novel polymeric flocculantand a method of dewatering with the same. The invention has thus beencompleted.

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] The invention will be explained below in detail.

[0010] In this description, an acrylate or methacrylate is referred toas a (meth)acrylate, and acrylamide or methacrylamide is referred to as(meth)acrylamide.

[0011] 1. Copolymer

[0012] The polymeric flocculant of the invention comprises a copolymerhaving alkoxyalkyl units or a poly(alkylene oxide) unit and furtherhaving water-soluble-monomer units. It is a water-soluble copolymer.When the copolymer contains a poly(alkylene oxide) unit, it is in theform of a block copolymer. Examples of the types of arrangement of thepolymer units include the AB type, ABA type, graft type, and others.

[0013] 1) Alkoxyalkyl Units

[0014] Examples of the alkoxyalkyl units include ones derived frommonomers such as methoxyethyl (meth)acrylate, ethoxyethyl(meth)acrylate, butoxyethyl (meth)acrylate, methoxypropyl(meth)acrylate, methoxybutyl (meth)acrylate, and the like. The copolymermay have units derived from two or more of these. Specific examples ofthe units include methoxyethyl units, ethoxyethyl units, butoxyethylunits, methoxypropyl units, methoxybutyl units, and the like.

[0015] The proportion of the alkoxyalkyl units in the copolymer ispreferably such that the proportion of the monomer(s) having analkoxyalkyl unit is from 0.5 to 40% by mole based on all monomers used.

[0016] 2) Poly(Alkylene Oxide) Unit

[0017] Examples of the poly(alkylene oxide) unit include units derivedfrom monomers such as ethylene oxide, propylene oxide, butylene oxide,and the like. The copolymer may have units derived from two or more ofthese. Specific examples of the unit include a poly(ethylene oxide)unit, poly(propylene oxide) unit, poly(butylene oxide) unit, and thelike.

[0018] A block copolymer containing a poly(alkylene oxide) unit can beobtained by using a poly(alkylene oxide) compound containing one or moreazo groups (hereinafter referred to as an azo RO initiator) or apoly(alkylene oxide) compound containing a photocleavable group(hereinafter referred to as a photo RO initiator) as a polymerizationinitiator and radical-copolymerizing one or more water-soluble monomersin an aqueous medium in the presence of the polymerization initiator. Bysuch methods, the target block copolymer can be advantageously producedwithout posing problems such as gelation, etc.

[0019] Preferred examples of the azo RO initiator include compoundshaving a unit represented by the following formula (1).

[0020] In formula (1), examples of R¹ include alkylene groups having 1to 4 carbon atoms, such as methylene and ethylene; examples of R²include alkylene groups having 1 to 4 carbon atoms, such as methylene,ethylene, and propylene; and R³ may be the same or different, andexamples thereof include a hydrogen atom, an alkyl group such as methyl,and a cyano group. Symbol m is 10 to 500, and n is 1 to 50, preferably 3to 20.

[0021] Examples of the terminal groups in formula (1) include a hydrogenatom, an alkyl group, and the like.

[0022] More preferred of the compounds having a unit represented byformula (1) are compounds represented by formula (2) given above. Symbolm is preferably 40 to 150, and n is preferably 5 to 10.

[0023] Preferred examples of the photo RO initiator include compoundshaving a unit represented by the following formula (3).

[0024] In formula (3), R⁴ represents a hydrogen atom, an alkyl groupsuch as methyl or ethyl, a hydroxyl group, a hydroxyalkyl group such ashydroxymethyl or hydroxyethyl, or a poly(alkylene oxide) group.

[0025] The poly(alkylene oxide) group is preferably one in which thenumber of repeating units is from 1 to 100, and is more preferably onein which the number of repeating units is from 10 to 50. Especiallypreferred examples of the poly(alkylene oxide) group are functionalgroups represented by the following formula (4).

[0026] In formula (4), R⁸ is an alkylene group having 1 to 4 carbonatoms, such as methylene, ethylene, or propylene; R⁹ is a hydrogen atomor an alkyl group having 1 to 4 carbon atoms; and s is 1 to 100,preferably 10 to 50.

[0027] In formula (3), R⁵ and R⁶ may be the same or different, andexamples thereof include a hydrogen atom, alkyl groups such as methyland ethyl, a phenyl group, alkoxy groups having an alkyl group having 1to 5 carbon atoms, such as methoxy and ethoxy, and cycloalkyl groupssuch as cyclohexyl. R⁷ is a hydroxyl group or a poly(alkylene oxide)group. The poly(alkylene oxide) group is preferably one having 1 to 100repeating units, more preferably one having 10 to 50 repeating units.Especially preferred examples of the poly(alkylene oxide) group arefunctional groups represented by formula (4) given above. In formula(3), at least either of R⁴ and R⁷ should be a poly(alkylene oxide)group. Preferred of the compounds represented by formula (3) are thecompounds represented by formulae (5) to (7).

[0028] In the case where the block copolymer is a graft copolymer, itcan be obtained by copolymerizing a macromonomer with one or morewater-soluble monomers in an aqueous medium. Examples of themacromonomer include: polyalkylene glycols having an ethylenicallyunsaturated group at one end, such as polyethylene glycolmono(meth)acrylate and polypropylene glycol mono(meth)acrylate;polyalkylene glycols having an ethylenically unsaturated group at oneend and an alkoxy group at the other end, such asω-(meth)acryloyloxypolyethylene glycol monomethyl ether andω-(meth)acryloyloxypolypropylene glycol monomethyl ether; and the like.

[0029] Although the proportion of the poly(alkylene oxide) unit in theblock copolymer may be suitably determined according to the desiredmolecular weight, it is preferably from 0.01 to 30% by weight, morepreferably from 0.1 to 20% by weight, especially preferably from 0.5 to5% by weight. When the proportion thereof is lower than 0.01% by weight,there are cases where the effects of improving filtration rate andreducing moisture content of dewatering cake are insufficient. When itexceeds 30% by weight, there are cases where flocculating strengthdecreases.

[0030] 3) Water-Soluble Monomer Units

[0031] Examples of the starting monomer(s) used for constituting thewater-soluble-monomer units include cationic monomers, anionic monomers,nonionic monomers, and the like. These monomers will be explained below.

[0032] (1) Cationic Monomers

[0033] Any cationic monomer can be used without limitations as long asit has radical polymerizability. The following compounds may be applied.

[0034] Examples thereof include: tertiary salts, e.g., hydrochloridesand sulfates, of dialkylaminoalkyl (meth)acrylates such asdimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, anddiethylamino-2-hydroxypropyl (meth)acrylate; tertiary salts, e.g.,hydrochlorides and sulfates, of dialkylaminoalkyl(meth)acrylamides suchas dimethylaminopropyl(meth)acrylamide; quaternary salts such ashalogenoalkyl adducts, e.g., chloromethyl adducts, and halogenoaryladducts, e.g., chlorobenzyl adducts, of dialkylaminoalkyl(meth)acrylates; quaternary salts such as halogenoalkyl adducts, e.g.,chloromethyl adducts, and halogenoaryl adducts, e.g., chlorobenzyladducts, of dialkylaminoalkyl(meth)acrylamides; and the like.

[0035] (2) Anionic Monomer Units

[0036] Any anionic monomer also can be used without limitations as longas it has radical polymerizability. The following compounds may beapplied.

[0037] Examples thereof include unsaturated carboxylic acids and saltsthereof. Specific examples include acrylic acid, methacrylic acid,crotonic acid, itaconic acid, maleic acid, and the like. Preferredmonomers in the invention are acrylic acid and methacrylic acid.

[0038] Examples of the salts of unsaturated acids include ammonium saltsand salts of alkali metals such as sodium and potassium.

[0039] (3) Nonionic Monomers

[0040] Examples of the nonionic monomers include acrylamide,methacrylamide, dimethylacrylamide, diethylacrylamide, methyl acrylate,ethyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylonitrile,vinyl acetate, and the like.

[0041] Those cationic monomers, anionic monomers, and nonionic monomersmay be used alone or as a mixture of two or more thereof.

[0042] In the case where the copolymer is a copolymer having alkoxyalkylunits, the proportion of the water-soluble monomer units in thecopolymer is preferably from 60 to 99.5% by mole based on all monomers.In the case where the copolymer is a copolymer having a poly(alkyleneoxide) unit, the proportion of the water-soluble monomer units in thecopolymer is preferably from 70 to 99.99% by weight, more preferablyfrom 80 to 99.9% by weight, especially preferably from 95 to 99.5% byweight, based on all monomers. In the water-soluble monomer unitsconstituting the copolymer of the invention, the proportions of theconstituent monomers are as follows. The proportion of the units derivedfrom cationic monomers or anionic monomers is preferably from 5 to 100%by mole, and that of the units derived from nonionic monomers ispreferably from 10 to 95% by mole.

[0043] 4) Processes for Producing the Copolymers

[0044] The copolymer containing alkoxyalkyl units in the invention canbe prepared by known polymerization methods for obtaining a polymer foruse as a polymeric flocculent or dehydrant.

[0045] A specific example thereof is aqueous solution polymerization. Inthis method, an aqueous monomer solution having a monomer concentrationof from 10 to 80% by weight, preferably from 25 to 60% by weight, ispolymerized in the absence of oxygen using a known polymerizationinitiator at a polymerization initiation temperature of from 0 to 35° C.and a polymerization temperature of 100° C. or lower for from 0.1 to 3hours to obtain a polymer.

[0046] Examples of the polymerization initiator include persulfates suchas sodium persulfate and potassium persulfate, organic peroxides such asbenzoyl peroxide, azo compounds such as 2,2′-azobis(amidinopropane)hydrochloride, azobiscyanovaleric acid, 2,2′-azobisisobutyronitrile, and2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], redox catalystscomprising a combination of hydrogen peroxide or sodium persulfate withsodium bisulfite or ferrous sulfate, and the like.

[0047] The block copolymer containing alkylene oxide units in theinvention can be prepared by known polymerization methods for obtaininga polymer for use as a polymeric flocculant or dehydrant. Preferredmethods include a method in which one or more water-soluble monomers arecopolymerized in an aqueous medium in the presence of an azo ROinitiator or photo RO initiator.

[0048] First, the case in which an azo RO initiator is used will beexplained.

[0049] A specific example thereof is aqueous solution polymerization. Inthis method, an aqueous monomer solution having a monomer concentrationof from 10 to 80% by weight, preferably from 25 to 60% by weight, ispolymerized in the absence of oxygen using an azo RO initiator at apolymerization initiation temperature of from 0 to 35° C. and apolymerization temperature of 100° C. or lower for from 0.1 to 10 hoursto obtain a polymer.

[0050] In this case, a combination with a polymerization initiator otherthan azo RO initiators can also be used according to need. Examplesthereof include the persulfates, organic peroxides, azo compounds, andredox catalysts mentioned above and the like.

[0051] Polymerization with ultraviolet may be conducted. For example, aphotopolymerization initiator of the ketal type, acetophenone type, oranother type may be used.

[0052] The amount of the azo RO initiator to be used may be suitablydetermined according to the degree of polymerization, viscosity, etc. ofthe target polymeric flocculent. It is usually preferred to use the azoRO initiator in an amount of from 0.5 to 5% by weight based on the totalamount of all monomers and the initiator.

[0053] In the case where the azo RO initiator is used in combinationwith another kind of initiator, the latter initiator is preferably onehaving a ten-hour half-life temperature higher than the half-lifetemperature of the azo RO initiator. In case where an initiator having alower half-life temperature is used, the result is a reduced blockcopolymer proportion, leading to poor effects of the invention.

[0054] The case in which a photo RO initiator is used will be explainednext.

[0055] Specifically, the target block copolymer can be obtained in thesame manner as in the process using an azo RO initiator described above,except that the polymerization initiator is replaced with a photo ROinitiator and polymerization is initiated by light irradiation at anintensity of from 0.5 to 1,000 W/m².

[0056] In this case, the reaction may be conducted either batchwise orcontinuously.

[0057] The amount of the photo RO initiator to be used may be suitablydetermined according to the degree of polymerization, viscosity, etc. ofthe target polymeric flocculant. It is usually preferred to use thephoto RO initiator in an amount of from 0.05 to 5% by weight based onthe total amount of all monomers.

[0058] In the case where the photo RO initiator is used in combinationwith another kind of initiator, the latter initiator is preferably onehaving a ten-hour half-life temperature higher than the half-lifetemperature of the azo RO initiator as in the case of the azo ROinitiator for the same reason as described above.

[0059] By conducting polymerization in the manner described above, ahigh-molecular water-soluble copolymer having an average molecularweight of from several millions to ten-odd millions can be obtained.However, the water-soluble copolymer of the invention is preferably onewhich has a 0.5% salted viscosity, as determined by the followingmethod, of from 5 to 200 mPa·s and a 0.1% insoluble content, asdetermined by the following method, of 5 mL or lower after washing.

[0060] 0.1% Insoluble Content:

[0061] A copolymer is dissolved in pure water to prepare 400 ml of a0.1% by weight (on a solid basis) solution. This solution is whollyfiltered through an 83-mesh sieve having a diameter of 20 cm. Theinsoluble matter remaining on the sieve is collected and the volumethereof is measured.

[0062] 0.5% Salted Viscosity:

[0063] A copolymer is dissolved in 0.4% by weight aqueous sodiumchloride solution to prepare a 0.5% by weight solution of the copolymer.The viscosity of the copolymer solution is measured with a Brookfieldviscometer after 5 minutes at 25° C. and 60 rpm.

[0064] The copolymer obtained by aqueous solution polymerization isusually in a gel state. It is chopped by a known technique, dried with aconveyor belt dryer, far-infrared dryer, or the like at a temperature ofabout from 60 to 100° C., and ground with a roll grinder or the like togive a powdery copolymer, which is subjected to use as a polymericflocculant after particle size regulation or addition of, e.g., anadditive thereto.

[0065] At the time of use, the polymeric flocculant of the invention maybe mixed with a known additive such as sodium hydrogen sulfate, sodiumsulfate, or a sulfamic acid as long as this does not adversely influencedewatering treatment.

[0066] 2. Method of Sludge Dewatering

[0067] When added to various sludges, the polymeric flocculant of theinvention forms flocs having an excellent balance among flocculatingstrength, filtration rate, and moisture content. There are no particularmethods for addition to sludges and for floc formation, and methods incurrent use may be applied satisfactorily.

[0068] The sludges to which the flocculant can be applied are notparticularly limited. Examples thereof include sludges resulting fromthe treatment of domestic sewage, sludges resulting from the treatmentof wastewaters from the food industry, sludge resulting from thetreatment of wastewaters from the chemical industry, sludges resultingfrom the treatment of piggery wastewaters, sludges from the pulp orpaper manufacturing industry, and the like.

[0069] Although the polymeric flocculent of the invention can be usedalone, it may be used in combination with an inorganic flocculant or anorganic cationic compound. Examples of the inorganic flocculant includealuminum sulfate, poly(aluminum chloride), ferric chloride, poly(ironsulfate), and the like. Examples of the organic cationic compoundinclude polymer polyamines, polyamidines, cationic surfactants, and thelike. Especially when the polymeric flocculent of the invention is anamphoteric polymeric flocculant, a method in which the polymericflocculant of the invention is added to a sludge to which an inorganicflocculant has been added is a more effective method of dewatering. Inthis case, it is preferred that after the addition of an inorganicflocculant, the pH be regulated to 4 to 8, more preferably 5 to 7.

[0070] The amount of the polymeric flocculant of the invention to beadded to a sludge is generally from 0.1 to 3% based on the dry solidcomponents of the sludge, and is preferably from 0.2 to 2% based on thedry solid components of the sludge. In case where the amount thereof issmaller than 0.1%, the recovery of suspended substances from the sludgeis insufficient. Even when the flocculant is used in an amount exceeding3%, no improvement in effect is observed.

[0071] The flocs formed can be dehydrated with a dehydrating apparatussuch as a screw press dehydrator, belt press dehydrator, filter pressdehydrator, or screw decanter to give a dewatering cake.

[0072] The flocculant of the invention is applicable also to a method ofdewatering with a granulating concentration tank having a filtrationpart.

[0073] Specific examples thereof include the following method. Aninorganic flocculant is added to a sludge, and this sludge is introducedinto a granulating concentration tank having a filtration part after thepolymeric flocculant is added thereto or together with the polymericflocculant. The filtrate is taken out of the filtration part and,simultaneously therewith, granulation is conducted. The granules aredehydrated with a dehydrator.

EXAMPLES

[0074] The invention will be explained below in more detail by referenceto Examples and Comparative Examples.

Example 1

[0075] Methoxyethyl acrylate (hereinafter referred to as MEA), anaqueous solution of the quaternary methyl chloride salt ofdimethylaminoethyl acrylate (hereinafter referred to as DAC), and anaqueous solution of acrylamide (hereinafter referred to as AM) wereintroduced into a Dewar vessel made of stainless steel in a proportionof 5.0/60.0/35.0 in terms of mol %, and distilled water was addedthereto so as to result in a total weight of 1 kg and an overall monomerconcentration of 47% by weight. Subsequently, the temperature of thesolution was regulated to 15° C. while bubbling nitrogen gas into thesolution for 60 minutes to thereby obtain an aqueous monomer mixturesolution for polymerization.

[0076] Subsequently, cupric chloride, azobisamidinopropane hydrochloride(trade name V-50; manufactured by Wako Pure Chemical Ltd.) as apolymerization initiator, and sodium hydrogen sulfite (NaHSO₃) wereadded in amounts of 0.3 ppm in terms of copper ions, 1,000 ppm, and 30ppm, respectively, based on the weight of all monomers to initiatepolymerization. The polymerization was continued for 1 hour in astationary state. Thereafter, the resulting water-soluble copolymer inan aqueous gel form was taken out of the Dewar vessel and chopped. Thegel chopped was dried at 80° C. for 5 hours and then pulverized toobtain the target polymeric flocculant.

Examples 2 to 4 and Comparative Examples 1 and 2

[0077] Polymeric flocculants were obtained in the same manner as inExample 1, except that the monomers, polymerization initiator, etc. werechanged to the conditions shown in Table 1. The polymeric flocculantsobtained were examined for 0.1% insoluble content and 0.5% saltedviscosity, and the results are shown in Table 1. In the table, AAindicates acrylic acid. TABLE 1 Comparative Example Example 1 2 3 4 1 2Polymeric flocculant A B C D F G MEA 5 10 15 5 0 0 DAC 60 60 60 30 60 30AM 35 30 25 35 40 40 AA 0 0 0 30 0 30 Monomer concentration 47 47 47 3647 36 (wt %) Polymerization 15 15 15 15 15 15 initiation temperature (°C.) Copper(II) (ppm) 0.3 0.3 0.3 0.3 0.3 0.3 V-50 (ppm) 1000 1000 10001000 1000 1000 NaHSO₃ (ppm) 30 40 40 10 40 10 0.5% Salted viscosity 3030 34 51 31 51 (mPa · s) 0.1% Insoluble 0 0 0 1 0 1 content (ml)

Examples 5 to 7 and Comparative Example 3

[0078] 200 ml of a raw sludge (SS, 13,500 mg/l; VSS, 9,500 mg/l)obtained from municipal sewage was placed in a 300 ml beaker. Any of thepolymeric flocculants synthesized in Examples 1 to 3 and ComparativeExample 1 was added thereto. The resulting mixture was stirred with ajar tester at 200 rpm for 1 minute to form sludge flocs. The particlediameters of the flocs were measured.

[0079] Thereafter, the sludge floc dispersion was gravitationallyfiltered through an 80-mesh net as a filter. The volume of the filtratewas measured after 10 seconds and this found value is shown asfiltration rate. The cake obtained was compressively dewatered with abelt press to determine the moisture content. The results of thesemeasurements are shown in Table 2.

Example 8 and Comparative Example 4

[0080] 200 ml of a sludge mixture (SS, 23,500 mg/l; VSS, 8,350 mg/l)consisting of a coagulated sludge and an excess sludge both obtainedfrom a wastewater from a chemical factory was placed in a 300 ml beaker.Poly(ferric sulfate) was added thereto until the pH became 4.5. Eitherof the polymeric flocculants prepared in Example 4 and ComparativeExample 2 was added thereto. The resulting mixture was stirred with ajar tester at 150 rpm for 2 minutes to form sludge flocs.

[0081] Subsequently, the sludge was stirred with a handy mixer at 560rpm for 15 seconds, and the particle diameters of the flocs formed werethen measured.

[0082] Thereafter, the sludge floc dispersion was gravitationallyfiltered through an 80-mesh net as a filter. The volume of the filtratewas measured after 10 seconds and this found value is shown asfiltration rate. The cake obtained from the sludge through filtrationwas dewatered with a centrifugal separator under the conditions of 2,000rpm and 10 minutes to determine the moisture content. The results ofthese measurements are shown in Table 2. TABLE 2 Comparative ExampleExample 5 6 7 8 3 4 Polymeric flocculant A B C D F G Optimal flocculant100 100 100 200 100 200 amount (ppm) Floc diameter (mm) 3-6 3-6 4-7 2-43-6 2-3 Filtration rate 118 152 156 130 130 120 (ml/10 sec) Moisturecontent of floc 70.5 70.1 68.5 79.5 71.5 79.4 (wt %)

[0083] As apparent from the Examples 5 to 7 and Comparative Example 3shown in Table 2, the moisture content decreased as the amount of MEAunits in the polymeric flocculant increased. It was further found thatthe MEA amounts not smaller than 10% by weight resulted not only in areduced moisture content but in a significantly increased filtrationrate.

[0084] It was found from Example 8 and Comparative Example 4 that theincorporation of 5 mol % MEA into a polymeric flocculant resulted in asatisfactory balance between filtration rate and moisture content.

Example 9

[0085] An aqueous DAC solution and an aqueous AM solution wereintroduced into a Dewar vessel made of stainless steel in a proportionof 60.0/40.0 in terms of mol %, and distilled water was added thereto soas to result in a total weight of 1 kg and an overall monomerconcentration of 46% by weight. Subsequently, the temperature of thesolution was regulated to 15° C. while bubbling nitrogen gas into thesolution for 60 minutes to thereby obtain an aqueous monomer mixturesolution for polymerization.

[0086] Subsequently, cupric chloride, an azo RO initiator [trade nameVPE-0201; manufactured by Wako Pure Chemical Industries, Ltd.; acompound represented by formula (2) given above wherein m is about 40 to50 and n is about 5 to 10], and sodium hydrogen sulfite (NaHSO₃) wereadded in amounts of 0.3 ppm in terms of copper ions, 1.4% by weight, and70 ppm, respectively, based on the weight of all monomers to initiatepolymerization. The polymerization was continued for 1 hour in astationary state. Thereafter, the resulting water-soluble copolymer inan aqueous gel form was taken out of the Dewar vessel and chopped. Thegel chopped was dried at 80° C. for 5 hours and then ground to obtainthe target polymeric flocculant.

[0087] The polymeric flocculant obtained was examined for 0.1% insolublecontent and 0.5% salted viscosity. The results of these measurements areshown in Table 3.

Examples 10 to 13 and Comparative Examples 5 to 7

[0088] Polymeric flocculants were produced in the same manner as inExample 10, except that the monomers, polymerization initiator, etc.were changed to the conditions shown in Table 3.

[0089] The polymeric flocculants obtained were examined for 0.1%insoluble content and 0.5% salted viscosity. The results of thesemeasurements are shown in Table 3. In the table, DMC indicates thequaternary methyl chloride salt of dimethylaminoethyl methacrylate, AAindicates acrylic acid, and V-50 indicates azobisamidinopropanehydrochloride [manufactured by Wako Pure Chemical Ltd.]. TABLE 3Comparative Example Example Polymeric 9 10 11 12 13 5 6 7 Flocculant A BC1 C2 C3 RA RB RC DAC 60.0 0.0 35.0 35.0 35.0 60.0 0.0 35.0 DMC 0.0100.0 0.0 0.0 0.0 0.0 100.0 0.0 AA 0.0 0.0 5.0 5.0 5.0 0.0 0.0 5.0 AM40.0 0.0 60.0 60.0 60.0 40.0 0.0 60.0 Monomer 46 75 36 36 36 47 75 36concentration (wt %) Polymerization 15 15 15 15 15 15 15 15 initiationtemperature (° C.) Copper(II) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 (ppm)VPE-0201 1.40 0.70 1.40 1.40 0.70 0 0 0 (wt %) V-50 (ppm) 0 0 0 100 5001000 1000 1000 NaHSO₃ (ppm) 70 80 35 25 15 30 60 10 0.5% Salted 26 17 6665 66 30 19 78 viscosity (mPa · s) 0.1% Insoluble 0 0 0 0 0 0 0 0content (ml)

Example 14

[0090] DAC, AM, and AA were introduced into a vessel made of glass in aproportion of 35.0/5.0/60.0 in terms of mol %, and distilled water wasadded thereto so as to result in a total weight of 1 kg and an overallmonomer concentration of 36% by weight. Subsequently, the temperature ofthe solution was regulated to 15° C. while bubbling nitrogen gas intothe solution for 60 minutes to thereby obtain an aqueous monomer mixturesolution for polymerization.

[0091] Subsequently, the photo RO initiator represented by formula (5)given above (n=20) was added thereto in an amount of 1,200 weight ppm ofall monomers. Using a 100-W black light, the resultant mixture wasirradiated from over the reactor at an irradiation intensity of 6.0mW/cm² for 60 minutes to conduct polymerization. Thereafter, theresultant water-soluble copolymer in an aqueous gel form was taken outof the Dewar vessel and chopped. The gel chopped was dried at 80° C. for5 hours and then ground to obtain the target polymeric flocculant C4.

[0092] The polymeric flocculent obtained was examined for 0.1% insolublecontent and 0.5% salted viscosity. The results of these measurements areshown in Table 4.

Example 15

[0093] A polymeric flocculant B2 was obtained in the same manner as inExample 14, except that the monomers, polymerization initiator, etc.were changed to the conditions shown in Table 4.

[0094] The polymeric flocculant obtained was examined for 0.1% insolublecontent and 0.5% salted viscosity. The results of these measurements areshown in Table 4. TABLE 4 Example 14 15 C4 B2 Polymeric flocculant DAC35.0 0.0 DMC 0.0 100.0 AA 5.0 0.0 AM 60.0 0.0 Monomer concentration (wt%) 36 75 Polymerization initiation 15 15 temperature (° C.) Copper(II)(ppm) 0.0 0.0 VPE-0201 (wt %) 0.0 0.0 V-50 (ppm) 0.0 0.0 NaHSO₃ (ppm)0.0 0.0 Photo RO initiator (ppm) 1200 600 0.5% Salted viscosity (mPa ·s) 70 15 0.1% Insoluble content (ml) 0 0

Example 16 and Comparative Example 8

[0095] 100 ml of a raw sludge mixture (SS, 15,500 mg/l; VSS, 12,400mg/l) obtained from municipal sewage was placed in a 300 ml beaker.Either of the polymeric flocculants produced in Example 9 andComparative Example 5 was added thereto. The resulting mixture wasstirred with a stirrer at 1,000 rpm for 30 seconds to form sludge flocs.The particle diameters of the flocs were measured.

[0096] Thereafter, the sludge floc dispersion was gravitationallyfiltered through an 80-mesh net as a filter. The volume of the filtratewas measured after 10 seconds and this found value is shown asfiltration rate. The cake obtained was dehydrated with a centrifugalseparator (4,000 rpm) for 1 minute to determine the moisture content.The results of these measurements are shown in Table 5 and Table 6.

Example 17 and Comparative Example 9

[0097] 200 ml of a raw sludge mixture (SS, 18,900 mg/l; VSS, 14,300mg/l) obtained from municipal sewage was placed in a 300 ml beaker. Anyof the polymeric flocculants produced in Example 10, Example 15, andComparative Example 6 was added thereto. The resulting mixture wasstirred with a stirrer at 200 rpm for 60 seconds to form sludge flocs.The particle diameters of the flocs were measured.

[0098] Thereafter, the sludge floc dispersion was gravitationallyfiltered to determine the filtration rate in the same manner as inExample 14. The cake obtained was compressively dehydrated with amini-belt press (areal pressure, 0.5 kg/cm²; three times) to determinethe moisture content. The results of these measurements are shown inTable 5 and Table 6.

Examples 18 to 21 and Comparative Example 10

[0099] 500 ml of a sludge (SS, 31,900 mg/l; VSS, 19,100 mg/l) obtainedfrom a wastewater from the paper manufacturing/pulp industry was placedin a 1 liter beaker. Aluminum sulfate was added thereto in an amount of3% by weight (based on the SS). Thereafter, any of the polymericflocculants produced in Examples 11 to 14 and Comparative Example 7 wasadded thereto. The resulting mixture was stirred with a stirrer at 100rpm for 90 seconds to form sludge flocs. The particle diameters of theflocs were measured.

[0100] Thereafter, the sludge floc dispersion was gravitationallyfiltered to determine the filtration rate in the same manner as inExample 16. The cake obtained was compressively dehydrated in the samemanner as in Example 1 to determine the moisture content. The results ofthese measurements are shown in Table 5 and Table 6. TABLE 5 Example 1617 18 19 20 21 22 Polymeric flocculant A B C1 C2 C3 B2 C4 Optimalflocculant 140 100 50 50 50 100 50 amount (ppm) Floc diameter (mm) 2-43-5 3-4 3-4 2-4 3-5 3-4 Filtration rate 55 136 150 143 135 132 152(ml/10 sec) Moisture content of 84.7 74.7 66.1 66.5 66.5 74.0 66.0 floc(wt %)

[0101] TABLE 6 Comparative Example 8 9 10 Polymeric flocculant RA RB RCOptimal flocculant amount (ppm) 140 100 50 Floc diameter (mm) 2-4 3-43-4 Filtration rate (ml/10 sec) 45 111 120 Moisture content of floc (wt%) 86.7 76.0 66.9

[0102] As apparent from comparisons between Example 16 and ComparativeExample 8, between Examples 17 and 21 and Comparative Example 9, andbetween Examples 18 to 20 and 22 and Comparative Example 10, thepolymeric flocculent of each Example attained an excellent filtrationrate and a reduced moisture content of flocs as compared with thepolymeric flocculants of the Comparative Examples. Incidentally, whenthe moisture content of flocs decreases by 2% by weight, the amount offuel oil to be used in the later step of incineration can be reduced by10% by weight.

INDUSTRIAL APPLICABILITY

[0103] The polymeric flocculant of the invention produces such anexcellent effect in sludge dewatering that it enables the formation offlocs having an excellent balance among flocculating strength,filtration rate, and moisture content.

1. (Amended) A polymeric flocculant which comprises a block copolymerproduced by copolymerizing one or more water-soluble monomers in anaqueous medium in the presence of a poly(alkylene oxide) compound havingone or more azo groups or a poly(alkylene oxide) compound having aphotocleavable group.
 2. (Amended) The polymeric flocculant of claim 1,characterized in that the water-soluble-monomers comprise cationicmonomers.
 3. (Amended) The polymeric flocculant of claim 1,characterized in that the water-soluble monomers comprise cationicmonomers and anionic monomers.
 4. A method of sludge dewateringcharacterized by adding the polymeric flocculant of any one of claims 1to 3 to a sludge after or without adding an inorganic flocculent or anorganic cationic compound thereto and then dewatering the sludge. 5.(Amended) A process for producing a block copolymer for use as apolymeric flocculant, characterized by copolymerizing one or morewater-soluble monomers in an aqueous medium in the presence of apoly(alkylene oxide) compound having one or more azo groups.
 6. (Added)A process for producing a block copolymer characterized bycopolymerizing one or more water-soluble monomers in an aqueous mediumin the presence of a poly(alkylene oxide) compound having aphotocleavable group.